Move DescriptorCache writing to WalletBatch

Instead of adhoc writing of the items in DescriptorCache, move it all
into WalletBatch.

src/wallet/scriptpubkeyman.cpp

@@ -1807,17 +1807,8 @@ bool DescriptorScriptPubKeyMan::TopUp(unsigned int size)
         }
         // Merge and write the cache
         DescriptorCache new_items = m_wallet_descriptor.cache.MergeAndDiff(temp_cache);
-        for (const auto& parent_xpub_pair : new_items.GetCachedParentExtPubKeys()) {
-            if (!batch.WriteDescriptorParentCache(parent_xpub_pair.second, id, parent_xpub_pair.first)) {
-                throw std::runtime_error(std::string(__func__) + ": writing cache item failed");
-            }
-        }
-        for (const auto& derived_xpub_map_pair : new_items.GetCachedDerivedExtPubKeys()) {
-            for (const auto& derived_xpub_pair : derived_xpub_map_pair.second) {
-                if (!batch.WriteDescriptorDerivedCache(derived_xpub_pair.second, id, derived_xpub_map_pair.first, derived_xpub_pair.first)) {
-                    throw std::runtime_error(std::string(__func__) + ": writing cache item failed");
-                }
-            }
+        if (!batch.WriteDescriptorCacheItems(id, new_items)) {
+            throw std::runtime_error(std::string(__func__) + ": writing cache items failed");
         }
         m_max_cached_index++;
     }

src/wallet/walletdb.cpp

@@ -248,6 +248,23 @@ bool WalletBatch::WriteDescriptorParentCache(const CExtPubKey& xpub, const uint2
     return WriteIC(std::make_pair(std::make_pair(DBKeys::WALLETDESCRIPTORCACHE, desc_id), key_exp_index), ser_xpub);
 }
 
+bool WalletBatch::WriteDescriptorCacheItems(const uint256& desc_id, const DescriptorCache& cache)
+{
+    for (const auto& parent_xpub_pair : cache.GetCachedParentExtPubKeys()) {
+        if (!WriteDescriptorParentCache(parent_xpub_pair.second, desc_id, parent_xpub_pair.first)) {
+            return false;
+        }
+    }
+    for (const auto& derived_xpub_map_pair : cache.GetCachedDerivedExtPubKeys()) {
+        for (const auto& derived_xpub_pair : derived_xpub_map_pair.second) {
+            if (!WriteDescriptorDerivedCache(derived_xpub_pair.second, desc_id, derived_xpub_map_pair.first, derived_xpub_pair.first)) {
+                return false;
+            }
+        }
+    }
+    return true;
+}
+
 class CWalletScanState {
 public:
     unsigned int nKeys{0};

src/wallet/walletdb.h

@@ -246,6 +246,7 @@ public:
     bool WriteDescriptor(const uint256& desc_id, const WalletDescriptor& descriptor);
     bool WriteDescriptorDerivedCache(const CExtPubKey& xpub, const uint256& desc_id, uint32_t key_exp_index, uint32_t der_index);
     bool WriteDescriptorParentCache(const CExtPubKey& xpub, const uint256& desc_id, uint32_t key_exp_index);
+    bool WriteDescriptorCacheItems(const uint256& desc_id, const DescriptorCache& cache);
 
     /// Write destination data key,value tuple to database
     bool WriteDestData(const std::string &address, const std::string &key, const std::string &value);